Coming back to init state after ng-click in ng-repeat?

I'm facing an issue due to my very low understanding of basic AngularJs concepts (I think). I have a list of clickable words. When I click on them, they change color (individually) through the use of Bootstrap 'labels' classes. It works fine BUT... (here it is :) ) : If I click my 'Try again' button, I am unable to set my colors back to the init state because I am unable to set 'this.selected' to 'false'... See the below code.

I'm sure it's not that difficult, but I'm stuck so if anyone could give me a hint, I'd appreciate.